rpenmanparker 

Maybe not, but most likely you have been riding internal cam skewers like Shimanos and Campagnolos until now...and the Mavics. They have a much stronger grip than external cam skewers like the light weight models even big name ones like Enve. It is just the inferior design. You have to put a lot more force into the clamping in order to get the same grip on the dropouts. Also check that the threads on your skewer rod and nut are deep enough to hold under high tension. You may have just bought a crappy pair. Most people can get external cam skewers to do the job, but every now and then someone just can't make them work, especially on horizontal dropouts. External cam skewers were never intended for anything but vertical dropouts.